fix: Require drupal/webpage and import the admin theme's block placements

Problem/Motivation

recipe.yml applies the webpage recipe but composer.json never required drupal/webpage, so applying the recipe failed. The recipe also sets default_admin as the site theme, but that theme's block placements are optional config a recipe doesn't install, so sites had no page titles, messages or tabs.

Steps to reproduce

Apply the webapi_starter recipe on Drupal 11.4.7.

Proposed resolution

Require drupal/webpage in composer.json and import default_admin's block placements config. Verified fixed on Drupal 11.4.7.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ❌ Reviewed by a human
• ❌ Code review by maintainers
• ❌ Full testing and approval
• ❌ Credit contributors
• ❌ Review with the product owner
• ❌ Update Release Notes
• ✅ Release

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

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